Preparation of ammonium sulphate



Jan. 8, 1935. R. RLFULTON PREPARATION OF AMMONIUM SULPHATE Filed'Sept. 5, 1951 2 Sheets-Sheet l INVENTOR. PoberfEFa/ia/Z A UK Y.

Jan. 8,1935. R. R. FULTON 1,986,889

7 PREPARATION OF AMMONIUM SULPHATE Filed Sept 5, 19:51 2 Sheets-Shet 2 TE TAT NT OFFICE? i "1,986,889 up PREPARATION OF VAMMONIUM SULPHATE Robert R. Fulton, Pittsburgh, 1%.,- assignor to The Koppers Company of Delaware, a corporation of Delaware Application September 5, 1931, Serial 3163611415 This invention relates to processes of preparing ammonium sulphate. An object ofthe 'presentinvention is to provides. process of preparing ammonium sulphate by the oxidation of ammonium sulphite. Another objectis to. provide improvements in methods of oxidizing ammonium sulphite so as to make. feasible-the seiiicient production of ammonium sulphate therefrom on a commercial scale. i 1 V I have found in the manufacture of ammonium sulphate by the oxidation of ammonium sulphite,

particularly when the latter is: in solution, that when the oxidizing gas is finely dispersed'substantially throughout the body of. the solution treated, increased yields or ammoniumisulphatej are obtained. It is particularlyadvantageous to have the gas in afinely dividedlstateat the place at which the gas is introduced .iintothe solution. oxidizing gas is preferably introducedat the .'base ofa relatively talljcolumn of the liquid containing ammonium sulphite for the purpose of takl 1 ing advantage of the hydrostatic pressure. This increased pressure at thelbase combinedflwithithe introduction of oxidizing gas in extremely "finely divided. condition in a region at the base of the column brings about'rapid oxidation of theammonium sulphite. The column is preferablyof such a height that substantiallyno union of .the gasbubbles occurs in the upper regions of the column.

Good results are obtained by treating an alkaline solution of sulphite, but the present process vary the hydrogen operates more efiiciently'whenthe sulphite solution is neutral or preferably in acid condition while "contacting with an oxidizing gas. The

preferred pH value is from about 5.5 to 7.0. Ammonia-containing gases or "sulphur dioxide-containing gases may be pa'ssedinto the sulphite solution intermittently or continuously either to ion concentration or to maintain it constant. 1

Other features' of the present invention will be i set forth in a further description of'the process which may be carried out in apparatus such as "that'shown byway 'of examplein the accompanying drawings; in which,--

. Figure 1 is a verticalsectional view partly in elevation of one form of apparatus, and

Fig. 2 is an elevational view, partly. in cross section of another form of apparatus.-

In the apparatusshown in Fig. 1, a solution containing ammonium sulphite is passed into a tall narrow column 1 through aipipe 2 controlled by a valve 2" near the base of the column or into 5 Claims. (01. 23-119) the top through a pipe 3controlled by a VaIveB".

Columns from. six feet to about sixty feet in height andup to tenfeet or more employed. 2

The column is filled to any desired level with solution containing ammonium sulphite, l 1 An oxidizing gas such as air, ionized air, oxygen, or 'gases containingoxygen or ozoneuare -made offrittedglass or the fine grades of alundum plates are suitable. The rate of-passage of the gas must be ;kept below that at which the gas tends to lift the solution bodily out of the column; butlthe rate is high enough to keep the solution in a foaming state. A meter 7 isiprovided for measuring gas. e

The pressure employed,forforcinghthe oxidizing gasthrough the porous plate and the column of solution, depends upon the fineness'of the pores in the plate and .upon the height of the column. Means are provided for recirculating gas ,or solution or both throughthe column 1. During the passage of gas into the solution, the latter passes out near the top of the column, downwardly through a pipe 8 andback into the bottom of the column through the turned-up end .9 of the pipe 8. I i

The gas passing upwardly through thesolution, collects in a chamber 10 at the top of the column l and is withdrawn; either through a pipe 11 controlled by a valve 12, or by closing the valve 12 the gas is -passed into a pipe 13 controlled by a. valve 14 and by means of a pump ;l5. is forced into the pipe. 5 and throughl"-the plate 4 into the solution in the column .1. 3

The. alkalinity .or acidity offlthe ammonium sulphite; solution in the column'may .be con trolled by admitting ammonia-containing gas or admitted separately into the pipe 5. ';To prevent in width are deposition of solid ammonium saltg 'after. am-

monia has been fed into the pipe '5gthrough a pipe 17 for instance, controlled ,by a valve 18, the ammonia gas is swept through the plate. 4

'valves, the proportions of the gases may be conthrough the porous plate along with the stream of oxidizing gas either intermittently orcontinuously. By the proper regulation of the trolled.

The gases before leavingfqhe tQhDi i nqQ l ll h is preferable to-increase the pressure in the later 1, and particularly if they are" withdrawn through the pipe 11, may be sprayed by means. of a spray 21 controlled by. a yalye, vith monia solution or with acid sulphite solution or dilute sulphuric acid depending on the sulphur dioxide or ammonia content of the gases.

. Pressur ;'th f empe tur s;

The temperature of the solution inthewolw if desired, is controlled by any suitable 31m I means. If the temperature used is above atmospheric; aheatingj'acket 23, for instance, is used. Steam-oi" other heating fluid is admitted through apipe 24 controlled by a valve 25 and withdrawn through ajpipe26' controlledby a valve 27. A pipe 28 controlled by a' valve 29' may be provided for-withdrawal of condensates. The heating fluid maybe substituted by a cooling-fluidif necessary. 'A' thermometer 30 provided for determining the, temperature of the solution infthe column 1. I

Good results are obtained bymaintaini'ng a temperature during oxidation of substantially 30."- C. to 45 C; Temperatures as high as'60 C.

'oreven 0. may beem ioy driwhencom.

ducting the, oxidation under; uperatmespheric i even 1 be higher an" h se iment n dr.. I 4 4, is temperature oithe solution'in the-column may; also be controlled by withdrawing heated solution through a pipe 31 controlled by a {valve 32,:and by passing in solution of lower tem'peraturethrough" the pipe 2; or the pipe '3 or through both; The concentration of the solution in the column mayalso,be controlledin this way.

Jfiplutiohsfcontainingi various proportions of ammoniuni'sulphite or ammonium bisulphite' or both. maybetreated; Solutions containing substantially to ammonium sulphite give satisiactqr'yyields of a mon um su ph H W" ever, a highl' satisfactory rnethodjis 'to' 'treat solutions atsuch" temperatures that when cooled to lower temperatures; a supersaturated solution of ammonium'sulphate forms'and crystals of this saltrea'dily separate out.

In-the latter'case the solution iswithdrawn from time to time through the pipe 31 and passed into'a drain table 33 to permit settlinglout of crystals -otammonium sulphate. i The solid ammonium sulphate 34:"With adhering mother liquor-ispassed-into-a centrifuged?) and the dried'ammonium sulphate is'then ready fo'r ship:- ment.

The; mothe'rdi'quor from the drain table 33 drains out through a pipe'36 and'is joined in a tank 3'? with liquor coming. from the centrifuge SB-throug-h a pipe'38; The mother liquor in the tank 3'7 is pumped by means of a pump 39 through apipe 40 into the-top of thecolumn l. v

- It has been found'thatthepresence of ammonium sulphate'in the sulphite solution is highly beneficial and'aids in the more rapid and complete'oxidationof the sulphit'el A sulphite solution containing up to about't35% and preferably not more than substantially 40% ammonium By. main- -'1 process may be carried on at any pressure, particularly atatmospheric pressure and above, it

stages-ofg the conversion. The last traces of am- ,sulphiteare difficult to convert to sulphate; 10111311357 ingreasing the pressure, per

cent conversion is obtained. Alternatively, the

addition of a smalla'mount of sulphuric acid, se gves to change traces of sulphite to sulphate.

In the apparatus-shown in Fig. l, the pressure in the column 1 is built up. by closing the valve 12 in the pipe 11, forcing oxidizing gas into the column through thepipe 5 until the desired pressure is reached, and thenpclosingthe. valve 6.

The valve 14 in the pipe 13 is opened and the gas 1;

is repeatedly circulated .through the solution by means of the pump' 15; I

Pressures .in the lower regions and at the bot? tom of the column maytberaised or lowered .by

varying the height of the column of solution treated. The column 1 may befilled toa relatively low level at the beginning. of theiprocess and afterv the reaction has proceeded fora time, the levelmaybe raised bythezaddition of .fresh sulphite solution or previously aerated solution. Forinstance'; in some casesa saturated solution of ammonium sulphate may b'e'added or atsolution of. substantially .the same. composition as that :whichis being treated in the column, may be added J A trough 41 is provided'to catch anyliquid which flows over thea top of. the colum-nl and the overflow is drawn 01T=througha seal'42. 1 The sulphur dioxide used in the present process mayitbeiderived from varioussourcesas forin-. stance by roasting metallic sulphides, or .byburning sulphur'or hydrogen sulphide.

The ammonia may be synthetic ammonia,.or ammoniaobtained by treating ammonium compounds with alkali or alkalineearth hydroxides,

. Crude ammonia liquors from coal .gas plants contain besides ammonium hydroxide, varying amounts of sulphides, and cyanides as well, as organic, materialssuch as pyridine, tar acid oils, na h hal ne nd. herwmp undsh a .ing ammonia. liquors, it is highly; advantageous to; remove the oily materials present therein. These materials tend to retardthe' oxidation The se t0.- h. ists and y be removed from the liquid in the column 1 by permitting them to overflowinto the trough 41.

Also, when treating ammonia liquors, it is advantageous to add sulphur dioxide in excess of the amount required to neutralize the ammonia and other alkaline-substances, in order to, decompo th ul h d sand Q a e which are driven off later as hydrogen sulphide andshydr senty nida I th e uqr left alkaline, the sulphides and cyanides form thiosulphate and thiocyanate which are undesirable impurities in ammonium sulphate. Further-.- more when the liquor is acid, theeffect of p ridine is eliminat d insey tis. onvert d to F A sajdi prs anacid medium; r

{ The presencepffl'certain impurities in aqua ammonia, such as primary amines, causes the formation of formalde hyde in thevery lasfstages of-the oxidationperiod. The detection of the period and for some purposes the oxidation may be stopped at this time. i

In the apparatus shown in Fig. 2 a series arrangement of columns is shown; Although only two columns 45 and 46 are "shown, any number may be used. The columns ishown are con-{ structed similarly to the column shown in Figil and are provided with heating jackets 47 and 48, and porous plates 49 and 50 attheir respective bases. l 3 Solution to be treatedis passedinto the cal- 52. The solution is withdrawn from the bottom of the column and by ,means ofia pump53 is pressure is reached after which the autoclave 'may be sealed and the mixture of gas and solupumped into. the top through a pipe 54. This recirculation maybe kept up until any desired stage of oxidation has been reached and then passed into the topof the column 46 through a pipe 55 for further treatment. By proper manipulation of the valves 56 and 57 the liquid stream passing'through the pipe 54 may be divided in any ratio.

The liquid may be maintained at a higher temperature in the column 46 than the liquid in the column 45 and may be recirculated by. pumping it from the bottom to of a pump 58 through a pipe 59. It maybe noted here that the oxidizinggas and sulphite solution travel countercurrently in the towers ,shown in Fig. 2 and concurrently in the tower shown in Fig. 1.

The oxidizing gas is passed into'the bottom of the column 46 through a pipe 60 controlled by a valve 61, out of the top ofthe column 46 and into the bottom of the column 45 through a pipe 62. By proper control, if air is used as the oxidizing gas, the gas leaving the top of r the column 45 through a pipe 63 provided with a valve 64, is substantially allnitrogen. Pipes 65 and 66 provided respectively with valves 67 and 68,\resp ectively conduct ammonia containing gas and" sulphur dioxide-containing gas into the pipe 66. Pipes 69and 70 provided respectively with valves 71 and 72, respectively conduct ammonia-containing gas and sulphur dioxide-containing gas into the pipe 62.

Treated solution containing ammonium sulphate is withdrawn from the topof the column 46 through a pipe 73 controlled by a valve 74 and passed into an -evaporator '75. provided with the usual heating means 76. Solution mayalso be passed from the bottom of the column to the evaporator through the pipe 59, through a pipe 7'7 provided with a valve 78, and then through a part of the pipe 73.

The slurry formed in theevaporator '75 iswithif drawn through a pipe 79 by opening a valve '80 and is. passed to a centrifuge 81 from which practically dry ammonium sulphate 82 is obtained. i 3

"Various modifications may be, made in the process and apparatus described. and. various types of apparatus may be. employed inthe present process. As a means for distributing the oxidizing gas in the sulphite solution, propellers may be mounted forrotation in the bottom of mixtureof finely first traces of formaldehyde serves as an indication of practically the end. of the oxidation the top by m an the column of solution above a gas inlet. By

solution. Another means for injecting oxidizing gas into rotating the propeller the gas is beaten into the the sulphite solution is a perforated pipe. Howfor the columnsas shown, heatedoxidizing gas may be injected into the solution, wherebydirect heating is accomplished. If the temperature of the solution rises aboveany desired point, cooled gases may be injected to lower the temperature.

To carry on the present process under pressure throughout the oxidation stage or duringany portion thereof, the sulphite-containing solution may be placedinautoclaves provided with an inlet and outlet for oxidizing gas. The gas may be admitted until a desired superatmospheric tion agitated by means of paddles or by rotation of the autoclave.

If desired, the oxidation of the ammonium sulphite may be carried on in the presence of a catalyst. The catalysts may be gaseous, liquid or solid substances. Y

The addition of foaming agents to the sulphite solution greatly improves dispersion of the oxidizing gas. The addition of as little as two grams of licorice root extract or saponin in twenty-five gallons of solution is very effective.

I claim as my invention:

1. A process of preparing ammonium sulphate, which comprises introducing an oxidizing gas into a solution containing ammonium sulphite in a closed chamber and thereby building up prese preferred and are employed sure thereinand thereby converting a major portion of the sulphite to sulphate, andthereafter discontinuing the introduction of oxidizing gas and converting the remainder of the sulphite to sulphate by recirculating the gas contained therein under the so built-up pressure through the solution.

l 2. A process of preparing ammonium sulphate,

which comprises introducing an oxidizing gas in finely divided condition into a solution containing ammonium sulphite and thereby converting a major portion of the sulphite to sulphate, increasing the pressure in the later stages of conversion and thereby continuing conversion as aforesaid and thereby converting the remainder undersuchincreased pressure;

,3. A process of preparing ammonium sulphate,

which comprises introducing an oxidizing gas in finely divided conditioninto the bottom of a column of liquid containing ammonium sulphite and thereby converting a major portion of sulphite to sulphate, and adding a small amount of sulphuric acid to the column during the introduction of the oxidizing gas to change last traces of sulphite to sulphate.

4. A process of preparing ammonium sulphate,

which comprises introducing an oxidizing gas into liquid containing ammonium sulphite and ammonium sulphate in a finely divided condition at the place at which the gas is introduced into the liquid and thereby converting the ammonium sulphite to ammonium sulphate, and maintaining the proportion of ammonium sulphate in the liquid fromabout 30% to 40% during the conversion,

and maintaining the height of the; hydrostatic head of such height that substantially; no union ,of gas bubbles occurs in the upper regions of the hydrostatic column.

A pro s of repa a nmoni m p at, which comprises introducing an oxidizing gas into a; solution 1 under pressure 1 and containing ammonium-sulphite and thereby converting the ma- ;nosaseo I jor portion of I the -sulphite to sulphate, and thereafter discontinuing the introduction of oxidizing gas and converting the remainder of the sulphite to sulphate by recirculating the gas contained therein through the solution under increased pressureu ROBERT R. FULTON. 

